The present invention relates to an element generator for a dither matrix and a dithering apparatus using the same, and more particularly to a dithering apparatus to be used for improving the image quality in an image outputting device having a low gray-scale characteristic.
Generally speaking, image outputting devices can be classified into a static image outputting device and a dynamic image outputting device. The static image outputting device, e.g., a plotter, ink jet printer, dot printer or laser printer generates a motionless image, while the dynamic image outputting device, e.g., a television receiver and computer monitor, generates a time-variant image. For various reasons, the above image outputting devices are restricted in terms of gray scale. For example, the gray scale of a liquid crystal monitor is severely restricted due to the characteristics of the liquid crystal itself. Similarly, the gray scale of a dot printer is determined by the number of dots which can be represented in the unit area. Thus, most image outputting devices are restricted in terms of gray scale, due to a correlation between their own characteristics and the resolution required. In addition, the gray scale may also be restricted based on the limitations of an image signal processor for outputting. For example, if an original image signal to be processed is represented by eight bits but the image signal processor is limited to only four bits, the gray scale is thereby restricted.
It is apparent that a lower gray scale diminishes image quality accordingly. Specifically, false contour generation and mach band effects are prevalent phenomena in systems having a low gray scale and lead to reduced image quality. Therefore, various algorithms have been proposed for overcoming these phenomena; for example, dithering, which prevents image quality reduction by adding randomly distributed noise to the original image.
Conventional dithering, however, is performed by software, which leads to the reduction of the processing speed. In particular, when a dither element to be used in the dithering process is generated by software, the reduction of the image processing speed is significant. This reduction in processing speed is quite remarkable in the field of computer graphics and results in unacceptably slow processing speeds. Hence, for increasing the image processing speed, the look-up table technique is employed as a hardware implementation of the dither matrix. However, the cost involved with such a look-up table, which is generally implemented by ROM memory elements, is excessive.